Background noise eliminator



R. J. MONERNEY 2,893,281

BACKGROUND NOISE. ELIMINATOR Filed July 21, 1953 J I I AMPLIFIER IN V EN TOR.

United States Patent BACKGROUND NOISE ELHVIINATOR Roger J. McNerney, Buffalo, N.Y., assignor to The Rudolph Wurlitzer Company, North Tonawanda, N.Y., a corporation of Ohio Application July 21, 1953, Serial No. 369,325 6 Claims. (Cl. 84-1.14)

This invention is concerned with an electronic organ, particularly with a background noise eliminator circuit therefor.

Various types of tone generators are used in electronic organs. Generally, the most satisfactory type of tone generator is a vibrating metallic reed. Such a reed can be shaped to vibrate in such manner as to emulate the fundamental and harmonics of any given organ tone Without the necessity of combining or synthesizing circuits. As explained in Hoschke Patent No. 2,015,016, a metallic reed spaced from a cooperating pick-up element forms a capacitor with such pick-up element. The capacity of this capacitor varies with the spacing between the plates (i.e. the reed and the pick-up element), and this spacing varies in accordance with the vibration of the reed. A D.C. potential applied to the pick-up element thus produces A.C. oscillations on the reed when the reed is vibrated. These A.C. oscillations very closely resemble the auditory oscillations of a pipe organ and when these electrical oscillations are amplified and translated into an audible sound by a loudspeaker, they are indistinguishable from pipe organ tones.

Sound generation in a vibrating reed electronic organ can be controlled by applying potential constantly to the reeds, and by selectively vibrating the reeds by means of air blasts when it is desired to play selected notes. Sound generation also can be controlled by continuously vibrating the reeds by means of air blasts, and by selectively energizing the reeds which it is desired to play. An electronic organ with the latter arrangement is known as a continuous reed organ. Certain advantages are presented by this arrangement in that there is no time lag either at the inception or at the end of a note due to the inertia of the reeds, and construction of such an arrangement is substantially less expensive.

A problem of considerable magnitude is encountered in continuous reed organs. Vibrating reed electronic organs and electronic organs utilizing other types of electrostatic generators are inherently susceptible to noise pick-up particularly of static charges, and the musical tones generated are low voltage oscillations. Consequently, careful shielding is necessary, and even this is not completely eifective. This is due in part to the nature of the tone generators. Even when a note is not played, air is passed past the various reeds and associated pick-ups. The friction of the moving air causes static charges to be developed on the reeds and associated pickups, and these charges give rise to the generation of spurious notes. These spurious notes are of very low magnitude compared with the proper notes, but still would appear in the output of the organ loudspeaker as an annoying background hum particularly when no notes are played. Other factors also may contribute to the generation of background noise.

The general object of this invention is to eliminate background noise from an electronic organ, specifically an electronic organ of the continuous reed type.

Another object of this invention is to eliminate background noise from a continuous reed electronic organ by means of a bucking voltage.

A further object of this invention is to provide a continuous reed organ wherein compensating voltages are applied to the reeds to counteract spurious tones generated thereby.

Other and further objects of the present invention will be apparent from the ensuing description when perused along with the drawings wherein:

Fig. 1 is a perspective view illustrating a portion of an electronic organ embodying the principles of the invention; and

Fig. 2 is a schematic wiring diagram illustrating the principles of the invention.

A part of an electronic organ 10 embodying the prin ciples of the invention is shown in Fig. 1. This organ includes a cabinet 12 having a pair of keyboards 14 and a pedal clavier 16. A volume control or swell pedal 18 also is provided. Suitable stop switches (not shown) are presented at the left end of the organ for convenient manual manipulation. The organ 10 also includes a loudspeaker 20 for converting electrical oscillations into audible organ tones.

As illustrated in Fig. 2, the organ includes a plurality of treble tone generators 22 including vibratile reeds 24 and pick-up elements 26, only one of each being shown by way of illustration. Similarly, there is a plurality of bass tone generators 28 each comprising a vibratile reed 30 and a cooperating pick-up element 32. All of the treble reeds are connected in parallel, and all of the bass reeds are connected in parallel. All of the pick-ups are, in general, individually connected, and it is to be understood that there may be more than one pick-up associated with each reed in order to generate difierent types of oscillations corresponding to each reed.

Potential is applied to each treble pick-up element 26 through a filter 34 to control the build up and decay of potential, and hence the attack and decay of the musical tones generated. Each filter 34 includes an output con nection 36 directly connected to the pick-up element 26. The filter includes a capacitor 38 grounding the output connection 36, and a resistor 40 connected between the output connection 36 and a central point 42. This central point is grounded through a capacitor 44. The central point 42 is connected through a resistor 46 to an input connection 48, the latter being grounded through a resistor 50. The input connection 48 is connected to a switch associated with one of the keys of the keyboards 14, or with one of the pedals of the pedal clavier 16. In general, each filter is separately connected to a different switch, and each switch is operated by a difierent key.

The bass pick-up elements 22 similarly are individually connected through filters 52 to switches associated with the bass keys or with the pedals of the pedal clavier. The filters 52 are similar to the filters 34 and need not be described in detail.

All of the reeds 24 and 30 are continuously vibrated by any suitable blower and conduit means (not shown) and the playing of the individual notes is selectively controlled by switches associated with the keys of the keyboard 14 and the pedals of the pedal clavier 16.

All of the treble reeds 24 are connected in parallel by means of Wires 54 to a junction 56. This junction 56 is connected by means of a capacitor 58 to treble'input 60 of an organ amplifier 62. Similarly, the bass reeds 30 are connected in parallel by means of wires 64 to a junction 66, and this junction is connected by means of a capacitor 68 to the bass input of the amplifier 62. The treble and bass signals are combined and amplified in the amplifier 62 by means of any suitable or conventional electronic combining and amplifying means and are ap- 3 plied to the loudspeaker 20 by means of a suitable cable 72.

Means is provided for supplying a bucking signal to balance out background noise. This means includes a feed back circuit having a 'conn'ectionat' 74 supplied from one of the stages of the amplifier 62 and grounded through a potentiometer resistor 76. The sliding tap 78 on the potentiometer is grounded through a voltage divider including a series of resistors 80 and 82. The junction 84 between the resistors 80 and 82 is connected by means of a 'wire 86 'to'a junction point88. The junction point 88 is connected "by means of a resistor 90 to the junction 56 which is connected wall of the treble reeds in parallel. The junction 88 also is connected through a resistor 92 to the junction 66 which is connected to all of the bass reeds in parallel. The polarity of the signals fed back by the potentiometer 76, 78, voltage divider 80, 82, junction 84, wire '86, junction 88, and either'of the resistors 90 or 92 is arranged to oppose or buck pick-up or background noises appearing on the reeds 24 and 30. The feed-back voltage applied to the reeds is adjustable by movement of the sliding tap 78 and *is set so as "to be of sufiiciently high magnitude to balance out background noises, but is of sufiiciently low potential so as -not to reduce the generated notes substantially.

The example herein shown and described is for illustrative purposes. Various changes may be made in the structure "without departing from the principles of the invention insofar as such structure falls within the spirit and scope of the appended claims.

The invention .is hereby claimed as follows:

1. In a'continuous reed organ, the combination comprising a group of continuously vibrating wind driven treble reed elements, a group of continuously vibrating Wind driven bass reed elements, a plurality of pick-up elements each spaced from and capacitively cooperable with one of said reed elements, static electric charges tending to accumulate between said reeds and pickups due to the wind which-vibrates the reeds, means for selective'ly applying a DC. potential to one of each pair of elements, electronic amplifying means, means connecting the other of each pair of elements to said electronic amplifying means for amplifying the electrical oscillations 1 generated by said reed elements, means for trans formingthe amplified electrical oscillations into audible organ tones, means associated with said amplifier de veloping a bucking voltage, and separate means for applying bucking voltages to the treble elements and to the bass elements for reducing background noise.

2. In a continuous reed organ, the combination comprising a group of continuously vibrating wind driven treble reeds, a group of continuously vibrating wind driven bass reeds, a plurality of pick-ups each spaced from and capacitively cooperable with one of said reeds, static electric charges tending to accumulate between said reedsand pickups due to the wind which vibrates the reeds, means for individually and selectively applying a DC. potential to said pick-ups, an amplifier having treble and bass inputs, means for connecting said treble reeds'in parallel to said treble input, means for connecting said bass reeds in parallel to said bass input, means for transforming the electrical oscillations from said reeds amplified by said amplifier into audible organ tones, a negative feed-back circuit from said amplifier including a potentiometer, a voltage divider, means for connecting said voltage-divider to the sliding tap on said potentiometer, resistance means electrically connected to said treble reeds for applying a feed-back bucking voltage from said voltage divider to said treble reeds, and resistance means electrically connected to said bass reeds for applying a feed-back bucking voltage from said voltage dividers to said bass reeds, said bucking voltages reducing background noise.

3. In an electronic musical instrument, the combination comprising a plurality of treble tone generators, a plurality of bass tone generators, an amplifier having treble and bass amplifying channels, capacity means connecting said treble tone generators to the treble amplifying channel of said amplifier, capacity means connecting the bass tone generators to the bass channel of said amplifier, means for converting amplified oscillations from said amplifier corresponding to the musical tones into audible musical tones, a junction point, impedance means connecting said treble tone generators to said junction point, impedance means connecting said bass tone generators to said junction point, and negative feed-back means connecting said junction point to said amplifier for reducing hum.

4. An .electronic musical instrument as set forth in claim 3 wherein the negative feed-back means 'comprises a potentiometer connected between the amplifier and ground and having a sliding tap thereon, .a voltage divider comprising a resistance means connecting :said sliding tap to ground, and a connection between said voltage divider and the junction point.

5. In an electronic organ the combination comprising a wind-driven bass reed, a bass pickup'in capacitive relation thereto, means for applying an electrical potential to said bass pickup, a wind-driven treble reed, a treble pickup in capacitive relation thereto, meansfor applying an electrical potential to saidtreble pickup, anamplificr having bass and treble input means, means including acapacitor connecting said bass reed to said input means, means including a second capacitor connectingsaid treble reed to said input means, a pair of resistors connected in series between said bassreed and said treblexreedand connected together at a junction, and negative feedback means connected from said amplifier to said junction to apply a voltage to said reeds to buck static charges tending to accumulate thereon and thereby to reduce background noise.

6. In an electronic organ as set forth in claim 5 the combination wherein the feedback means comprises a potentiometer resistor connected from said amplifier to ground, a sliding tap on said potentiometer resistor, a pair of resistors connected in series from said 'tap to ground and connected together at a second junction, and means connecting said junction together.

ReferencesCited inthe file'of'this patent UNITED STATES PATENTS 2,015,014 Hoschke .Sept. 17, 1935 2,414,886 Miessner Jan. 28, 1947 2,495,809 Graham Jan. 31, 1950 2,508,586 Veneklasen May23, 1950 2,557,769 Schmidt June 19, 1951 2,568,797 Eland -Sept. 25, 1951 2,623,996 Gray Dec. 30, 1952 2,672,781 Miessner Mar. 23, 1954 OTHER REFERENCES Radio Engineering, by Terman, third edition, pages 311 to 326. 

